Purpose - Investigation of oil leakage paths from the engine seals into the gas path of jet engine compressors and the estimation of oil concentration in aircraft cabin air based on fundamental aircraft and engine parameters. --- Approach - Real jet engine illustrations were collected and used for a detailed investigation of possible paths of oil-contaminated air into the main gas stream of the jet engine compressor before the extraction of bleed air. Furthermore, an equation was analyzed to calculate the oil concentration in the cabin air. Required aircraft and engine and parameters were collected for five engines: CF34, V2500, CFM56, PW4000, and GE90 on typical aircraft. --- Findings - On the basis of the illustrations various oil leakage paths were identified. Regarding the oil concentration, it could be shown that larger engines tend to have lower oil concentration in the cabin air. If the position of the bleed port for bleed air extraction is located further downstream with respect to the engine seals, oil concentration is higher. --- Research Limitations - All investigations are based on common sense. The oil concentration in the cabin was calculated based on the assumption that 1 % of oil consumption goes into the cabin. --- Practical Implications - The influence of fundamental aircraft and engine parameters on oil concentration is better understood. These parameters are number of engines, engine air intake diameter, by-pass ratio, total number of bearings (seals) and their number upstream of the bleed port, oil consumption, cruise Mach number, and cruise altitude. --- Social Implications - People concerned about aircraft cabin air contamination can better argue their case with the information in this project. --- Value - It is an important step in the argument to show how the oil can find its way into the compressed air path. Before, it was just assumed that leaking oil from the engine seals will "somehow" make its way. The usefulness of the equation for oil concentration in the cabin air is shown now with an increased number of five engines instead of just one engine as before. This gives increased credibility to the equation.

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